The application of fluorene-based conjugated polyelectrolytes (CPEs) as electron injection layer for the fabrication of multilayer polymer light emitting diodes (PLEDs) has attracted much attention.1 As the interface between the emissive layer and cathode, the electron injection/transport ability would be influenced by the nanostructures of CPE films. However, since the most reported fluorene-based CPEs are either oligomers or polymers with alternative/random struclures,2 the morphology of CPEs can not be effectively controlled by common thermal-annealing or solution processing procedures.
To get well-organized film morphologies, a plausible method is to utilize copolymers containing immiscible multi-blocks which could potentially form ordered arrays in tens of nanometers.3. However, the synthesis of all-conjugated block copolyfluorenes is of great challenge, since the conventional aromatic coupling polycondensation procedure can not give well-defined molecular weight and low PDIs. The recent developed quasi-“living” Kumada reaction of Grignard-type monomers made it possible to synthesize polythiophenes,4 polyphenylenes5 polypyrroles6 and their block copolymers7 with controlled molecular weight and low PDI, however, this method was limited for synthesizing polyfluorene derivatives because of the unexpected chain transfer reaction.6b 8 
Recently, Yokozawa et al. reported an alternative quasi-“living” polymerization via Suzuki-Miyaura coupling reaction, which could achieve polyfluorenes with well-defined molecular weight and polydispersity (PDI) via chain-growth procedure.9 The polymerization was performed with the initiation of 7-bromo-9,9-dialkyl-9H-fluoren-2-yl-boric acid ester (MA or MB) by ′Bu3PPd(Ph)Br as arylpalladium(II) halide catalyst. Since the intermediate Pd(O) species could be intramolecularly transferred to the C—Br end group, the polymerization was supposed to proceed in a chain-growth procedure. In considering that the “living” end group could remain active before quenched, the polymer intermediate could act as “macro-initiator” to allow the formation of another block with the successive addition of monomers.10 